1. Field of the Invention
The present invention relates to a storage device for reading/writing data by floating a head with a flying head above a rotating recording medium, and particularly relates to a storage device, a control method, and a program for controlling the clearance between the head and the recording medium, the head-disk clearance to a predetermined target clearance by changing the projection distance protrusion value by thermal expansion accompanying heating of a heater provided in a head caused by electric power distribution.
2. Description of the Related Arts
Conventionally, the floating distance flying height of the head with respect to the recording surface of a magnetic disk has to be reduced in order to realize a high recording density of the magnetic disk device, and a floating distance flying height of 10 nm order is realized recently. However, when the floating distance flying height of the head is reduced, collision with minute protrusions on the magnetic disk surface is readily generated, and variation of the clearances between heads is present in the range of mechanical common differences; therefore, there is a problem that the floating distance flying height cannot be set lower than the range of common differences when the medium contact is taken into consideration. Therefore, recently, like JP2002-037480, there is proposed a method in which variation in the projection distance protrusion value (TPR distance) caused by a phenomenon in which the head floating surface protrudes toward the direction of the magnetic disk due to temperature increase in a write head (thermal protrusion: TPR) is measured in an examination process or the like and retained in a magnetic disk, and the data is used for managing the floating distance flying height for each head. Furthermore, there have also been proposed methods like JP2005-071546 and JP2005-276284 in which a heater is incorporated in a head, and the clearance between the head and the recording surface of a magnetic disk is controlled by utilizing the projection phenomenon caused by thermal expansion of the head floating surface accompanying electric power distribution to the heater. In JP2005-071546, a constant element temperature is maintained by changing the electric power applied to an electricity conduction film provided on the head with respect to increase in the device temperature or the element temperature due to recording/reproduction, thereby maintaining a constant clearance between the element and the recording medium. In JP2005-276284, a heating device for floating distance flying height increase, for increasing the distance between the recording reproduction element and the magnetic disk surface, by causing a part of an air bearing surface of the head to expand and project by heating, and a heating device for reduction in the floating distance flying height for reducing the distance between the recording/reproduction element and the magnetic disk surface by causing another part of the head air bearing surface to expand and project by heating are provided in the head, and the floating distance flying height is corrected such that reproduction can be performed without causing collision during device activation or the like. Moreover, as the method for measuring the changed distance of the clearance between the head of the magnetic disk device and the magnetic disk, a method utilizing the fact that reproduction amplitude lead from the space loss method of Wallace spacing loss is changed in accordance with the clearance is known (U.S. Pat. No. 4,777,544)
However, in such conventional methods of controlling the clearance between the head and the magnetic disk recording surface, basically, the projection distance protrusion value is adjusted such that reproduction can be performed without causing medium contact by utilizing that the clearance is changed due to expansion/projection of the head floating surface along with heating of the heater caused by electric power distribution; and there has been a problem that highly precise clearance control of controlling the clearance upon recording and reproduction to a constant target clearance by taking variation of the clearances which are different in each head into consideration cannot be performed. Moreover, in the conventional clearance measurement utilizing the space loss method of Wallace spacing loss (Wallace), the clearance is measured from amplitude change in a reproduction signal when the head is caused to float by activating the magnetic disk device in the state in which the head is in contact and stopped in a contact-start-stop area of the magnetic disk surface. However, in recent magnetic disk devices, contact-start-stop of the head is abolished, and a head retained in a ramp load mechanism is delivered to the disk surface upon activation of the device in the state in which the magnetic disk is rotating, thereby causing it to float from the beginning; thus, there is a problem that the amplitude change at the time when the head which is in contact with the magnetic disk surface floats cannot be detected, and the clearance cannot be measured from unchanged amplitude of the reproduction signal of the head which is floating with a constant clearance.